This invention relates to the field of pelletizers for food processors. In particular, this invention relates to the mounting of dies in a food pelletizer.
Pelletizers are well-known in the field of food and feed processing. A conventional pelletizer comprises a two part annular die housing supporting a cylindrical annular die. The die has a radially inner surface, a radially outer surface and annular shoulders projecting in opposite directions toward the die housing. Slots extend from the radially inner surface to the radially outer surface. Each part of the die housing supports an edge of the die. The die housing is rotatably supported from a frame. The die and die housing define an enclosed pelletizing chamber. Located within the pelletizing chamber are a series of rollers rotatably supported by a roller frame. The rollers are positioned by the frame to be in intimate contact with the radially inner surface of the annular die. The die housing is driven by a motor or other mechanism to rotate the annular die. The rollers, not being directly driven, but being in contact with the radially inner surface of the die, are caused to rotate by the rotation of the die. Conditioned feed material is introduced into the pelletizing chamber. The feed material is captured between the rollers and the radially inner surface of the die and extruded through the slots in the die. Knives or other means are located around the radially outer surface of the die to shear the extruded feed material from the radially outer surface of the die to form pellets.
In a conventional pelletizer, the die housing contacts the surfaces of the annular die shoulders and extends in a manner to form a lip in close contact with at least a portion of the outer radial surface of the die shoulder. In some designs, the die and die housing are in direct contact along the die shoulder and lip of the housing. Direct contact results in wear on both components. Reduction of wear of the components has been accomplished by hardening either or both of the die and die housing. As the components wear, they are re-machined for proper fit.
In other prior designs, a die mount is located between the radially outer surface of the die shoulder and the extended lip of the die housing. The die shoulder continues to contact the die housing. The die mount or wear, ring is employed to extend the operational life of a particular die. Vibration and flexing of the die and die housing during operation of the pelletizer results in wear of the die mount. The die mount is intended to take up the wear that would normally be experienced by the die and therefore extend the operating life of the die.
A conventional wear ring in a pelletizer is of cylindrical construction with a rectangular cross section. The longer axis of the cross sectional rectangle is parallel to an axis of rotation defined by the die mount, die and die housing. While employment of the die mount is superior to direct die to die housing contact, several disadvantages do exist from the conventional design. To preserve rotational balance, the die, die housing and wear ring must be manufactured to relatively high tolerances so as to fit well together and preserve rotational balance. The cylindrical die mount requires periodic remachining to maintain high tolerances and therefore proper balance. Even slight variations in manufacturing tolerances can result in misalignment of the components and the inability to secure the components together for operation of the pelletizer. Even during set up of correctly machined components, the large sizes of the die and die holder can easily result in misalignment of the components. Misalignment of the components produces destructive rotational imbalances during operation of the pelletizer.